Imaginal discs are the embryonic precursors of much of the adult cuticular structure of Drosophila. They are stimulated by Beta-ecdysone to undergo differentiation in vitro in completely defined culture medium. A first step in this differentiation is the evagination of leg and wing discs to form leg and wing appendages. Evagination is inhibited by a second insect hormone, juvenile hormone. Our overall objective is to describe on genetic, molecular and cellular levels the mechanism by which Beta-ecdysone and juvenile hormone act to regulate developmental processes in imaginal discs. During the current year our efforts have particularly involved studies on the cellular mechanisms involved in evagination, and formation of the pupal cuticle. Additionally, we have extended our studies on the role of the "sodium pump" (Na+/K+-dependent ATPase) in the action of ecdysone and juvenile hormone. BIBLIOGRAPHIC REFERENCES: Fristrom, J. W., Chihara, C. J., Kelly, L. and Nishiura, J. T. (1976) The Effects of Juvenile Hormone on Imaginal Discs of Drosophila In Vitro: The Role of the Inhibition of Protein Synthesis. In: The Juvenile Hormones, L. Gilbert, Ed. pp. 432-448. Plenum Press. Kiss, I., Gabor, B., Fodor, A., Szabad, J. and Fristrom, J. W. (1976). Prepupal Larval Mosaics in Drosophila melanogaster. Nature 262:136-138.